1. Field of the Invention
The invention relates to a process of cleaning food processing equipment, in particular membrane filters which are used for producing foodstuffs or for cleaning water, wherein the filters are contacted with a cyclic nitroxyl compound and a reoxidator, or with a cyclic nitroxonium compound.
2. Description of the Related Art
In the food industry, use is being made to an increasing extent of membrane filters, in particular plastic membranes such as polyvinylpyrrolidone, polysulphone, polyether-sulphone and certain types of polyamides, for removing undesirable insoluble matter from beverages and other liquids. Such membranes are also used for cleaning surface water. Such membranes ensure an expedient removal of undesirable constituents, in particular micro-organisms such as algae, fungi and bacteria.
The problem is, however, that such membrane filters become blocked even after a short time so that they become unusable. The blocked filters can be regenerated, for example by rinsing them through in the opposite direction. However, that is a complicated process and no longer effective in the long term because the contamination accumulates. In addition, it is difficult to remove some persistent organic contaminants in this way.
WO 97/45523 describes the use of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as nitroxyl compounds and hypochlorite and hypobromite as a reoxidator for cleaning beer-settling modules. The presence of halogen residues, especially bromine residues is highly undesired in equipment used for preparing or treating beverages and other foodstuffs. Also the effective life time of the filters and their tear strength are negatively affected by the presence of bromine compounds.
WO 99/15256 discloses the use of cyclic nitroxyl compounds such as TEMPO together with a calcium sequestering agent for cleaning filters to be used in purifying surface water.
The oxidation of carbohydrates and other primary alcohols with nitroxyl compounds and peracid, especially peracetic acid in the presence of catalytic amounts of bromine, is known as such from WO 99/57158.